Thin film dielectrics with perovskite structure and preparation thereof

ABSTRACT

Methods of making a ternary oxide and a perovskite-related ternary oxide structure are described. The methods include reacting a binary oxide with a metal oxide or a metal hydroxide to form a ternary oxide dielectric layer on a substrate. Powders, anodes, pressed articles, and capacitors including the ternary oxide or perovskite-related ternary oxide structure as a dielectric layer or other layers are further described.

This application claims the benefit under 35 U.S.C. §119(e) of priorU.S. Provisional Patent Application No. 60/495,220 filed Aug. 14, 2003,which is incorporated in its entirety by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to perovskite-related materials andmethods to make a perovskite-related structure, as well as to methods ofmaking ternary oxide dielectric films and capacitors and other devicescontaining the films.

Dielectric films or layers are used in a variety of applications, suchas anode production and capacitors. Typically, dielectric filmscomprised of binary metal oxides, such as Ta₂O₅ and Nb₂O₅, are formed ona metal substrate creating a metal-metal oxide interface. However, whenusing binary metal oxides, such as Ta₂O₅ and Nb₂O₅, the binary metaloxide can break down to form undesirable metal oxides, such as NbO2,which can then diffuse across the interface into the metal anode, forinstance. This is especially true in the case of Nb₂O₅, because theinterface involving niobium is particularly sensitive to time andtemperature. Moreover, the method for making the binary metal oxidesgenerally involves several steps, which increases production costs.

Conventional binary metal oxide films have several disadvantages. First,a thermodynamic instability can exist between the substrate and thebinary oxide dielectric interface, which often results in the formationof intermediate oxides. As a result of intermediate oxide formation,oxygen vacancies promote oxide-ion migration, which can affect thecritical performance characteristics of the host device. For example, incapacitors, oxygen-ion vacancies facilitate space-charge polarization,dielectric loss, and low breakdown voltage. The above conditions arecharacteristic of a non-uniform, non-coherent, and/or non-mechanicallysound dielectric film. Second, surface films of binary metal oxidesoften degrade, which affect the performance of devices into which thefilms are incorporated. Furthermore, high-temperature (e.g., above about300° C.) processing typically used in formation of binary metal oxidefilms enhances oxide mobility and favors comproportionation even at acomparatively stable Ta/Ta₂O₅ interface. Both the reaction product andthe enhanced oxygen mobility promote space charge polarization anddielectric loss.

With an ever-increasing demand for producing, at low cost, a dielectricfilm having a high thermodynamic stability of the substrate/dielectricinterface, it is an important priority to provide a one-stepperovskite-related ternary oxide film. Accordingly, a need exists toovercome one or more of the above-described disadvantages ofconventional dielectric films.

SUMMARY OF THE PRESENT INVENTION

It is therefore a feature of the present invention to provide a ternaryoxide dielectric perovskite-related ternary oxide structure.

Another feature of the present invention is to provide a dielectric thathas an increased thermodynamic stability at the substrate/dielectricinterface.

A further feature of the present invention is to provide a lowtemperature reaction to prevent or reduce oxide diffusion into thesubstrate when making the dielectric.

An additional feature of the present invention is to provide a lowtemperature reaction to prevent reaction of the substrate withimpurities or solvents when making the dielectric.

Also, a feature of the present invention is to provide a highmobility/diffusion coefficient during film formation to promote rapidreaction.

Another feature of the present invention is to provide a reasonabledielectric constant of a reaction medium to promote ionic surfacereactions.

Yet another feature of the present invention is to provide a dielectricfilm that is uniform, coherent, and stable.

Additional features and advantages of the present invention will be setforth in part in the description which follows, and in part will beapparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and attained by means of the elements andcombinations particularly pointed out in the written description andappended claims.

To achieve these objectives and other advantages and in accordance withthe purposes of the present invention, as embodied and broadly describedherein, the present invention relates to a method of making a ternaryoxide. According to one embodiment of the present invention, the methodincludes reacting a binary oxide with a metal oxide to form a ternaryoxide dielectric layer on a substrate, wherein the metal oxide isdifferent from the binary oxide. According to another embodiment, themethod includes reacting a binary oxide with a metal hydroxide to form aternary oxide dielectric layer on a substrate. According to anotherembodiment, the method includes reacting a binary oxide with a metalcarbonate to form a ternary oxide dielectric layer on a substrate. Othermetal materials can be used.

The present invention also relates to a method of making a ternary oxidedielectric by contacting at least one metal oxide and a binary oxidewith a supercritical fluid and/or with a supercritical fluid and aco-solvent.

The present invention further relates to a method of making a ternaryoxide dielectric by heating a metal material, for instance metalcompound, (e.g., metal oxide, metal salt, metal hydroxide, metal halide,metal carbonate, or metal nitrate) at a temperature and a pressuresufficient to melt the metal material to form a molten metal material;and contacting the molten metal material to a binary oxide that isdisposed on a substrate. The method may include stabilizing the film ofbinary oxide on the substrate, or the incipient ternary oxidedielectric, by the use of an applied voltage (faradaic or non-fardaic).

The present invention further relates to a method of making a ternaryoxide dielectric by fusing a binary oxide with a metal material (e.g.,metal hydroxide, metal oxide, or metal carbonate) to form a solidmaterial upon cooling; dissolving the solid material in a first solution(e.g., aqueous); disposing the first solution, or a derivative of thefirst solution onto the substrate; and heating the substrate with thefirst solution, or an evaporated film of the solution, disposed thereonunder vacuum. The substrate may be the metal constituting the binaryoxide, a binary oxide film on a metal, or a different metal.

The present invention further relates to a method of making a ternaryoxide dielectric by anodizing a binary oxide, wherein the binary oxidecomprises an anode, in an electrolyte. The electrolyte is constituted byhaving some solubility for metal oxides.

The present invention further relates to a method of making a ternaryoxide dielectric by anodizing a binary oxide, wherein the binary oxidecomprises an anode, and contacting the binary oxide with at least onemolten metal containing at least one dissolved oxide. The molten metalmay be molten alkali metals, alkaline earth metals, or mixtures thereof.

The present invention further relates to substrates with ternary oxidefilms and articles using or having the same.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention as claimed.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

A method of making a ternary oxide according to the present inventionpreferably includes reacting a binary oxide with a metal oxide to form aternary oxide dielectric layer on a substrate, wherein the metal oxideis different from the binary oxide. The method alternatively includesreacting a binary oxide with a metal hydroxide and/or metal carbonate toform a ternary oxide dielectric layer on a substrate. Other metalmaterials can be used. In the present invention, more than one type ofmetal material can be used, and/or more than one type of binary oxidecan be used.

For purposes of the present invention, a ternary oxide is any threeelement containing compound that is an oxide, for example, LiNbO₃,KNbO₃, KTaO₃, BaTiO₃, NaNbO₃, NaTaO₃, combinations thereof, and thelike. It can be represented by the formula, for example, AMO₃, where Acan be at least one alkali metal or alkaline earth metal and M is atleast one metal. The perovskite-related ternary oxide may also be asolid solution of one or more ternary oxides. The solid solution is nota mixture. A mixture can be separated by physical methods. Threeexamples are given. For example, the ternary oxide can be a solidsolution of NaNbO₃ and KNbO₃, which would be written asNa_(x)K_((1−x))NbO₃ by convention. In general, the stoichiometricvariable x can range from zero to one. The sites that normally holdsodium ions (Na⁺) are partially substituted for by potassium ions (K⁺).A second example is a solid solution of KTaO₃ and KNbO₃, e.g.,KTa_(x)Nb_((1−x))O₃. A third example is a solid solution of four ternaryoxides, e.g., Na_(x)K_((1−x))Ta_(y)Nb_((1−y))O₃. In the third example,the stoichiometric coefficients x and y are independent. For example,the coefficient x can be varied without altering y. In general, thevariable y can range from zero to one, including decimals thereof (e.g.,0.1, 0.2, 0.3, etc . . . ).

The binary oxide in the present invention can be any binary oxide (i.e.,any two element containing compound that is an oxide). The preferredbinary oxides in the present invention are transition metal oxides,refractory metal oxides, and/or valve metal oxides, that are capable ofreacting with a metal oxide to produce the desired ternary oxide.Examples of such binary oxides are TaO, NbO, Nb₂O₅, Ta₂O₅, and TiO₂.Other examples include other valve metal suboxides. It is preferred touse a high-purity binary oxide to avoid introduction of impurities whencontacting the binary oxide to the supercritical fluid containing themetal oxide. Accordingly, the binary oxide preferably has a purity of atleast about 95% and more preferably at least about 99% or more.

The binary oxide in the present invention can also be a solid solutionof two or more binary oxides. Here again, a solid solution is not amixture. An example for two binary oxides is a solid solution of Nb₂O₅and Ta₂O₅, which by convention can be written as Ta_(2x)Nb_((2−2x))O₅.Here again the stoichiometric variable x may take the values rangingfrom zero to one, including decimals thereof (e.g., 0.1, 0.2, 0.3, etc .. . ).

The substrate in the present invention, which can include the binaryoxide on its surface, can be any shape or size, such as, but not limitedto, plate, block, pellet, can, anode, filament, and the like. Thesubstrate can be a valve metal substrate, a refractory metal substrate,a conductive metal substrate, alloys thereof, and the like. Examples areTa, Nb, Al, Ti, Zr, and the like. The substrate can also be a valvemetal suboxide such as NbO and the like. Numerous examples are describedin U.S. Pat. Nos. 6,759,026; 6,462,934; 6,416,730; and 6,322,912. Thevalve metal suboxide typically has an atomic ratio of metal to oxygen of1: less than 2.5. The substrate can be a pressed metal substrate.Examples of such preferred substrates include foil or a sponge made frommaterials, such as Nb, Ta, and Ti. Substrates having a layer of binaryoxides are commercially available. Preferably, the metal present in thebinary oxide is the metal in the substrate. Preferably, the substrate ismade of pure metal or alloys thereof or oxides thereof with or withoutdopants present. The substrate can be an anode or pressed powder. Allpatents/publications mentioned herein are incorporated in theirentireties by reference herein.

The metal oxide used in the present invention can be in any shape orsize. Preferably, the metal oxide has a shape and size sufficient to atleast partially be soluble or suspended in a supercritical fluid. Themetal oxide can be dissolved, at least partially, in the supercriticalfluid. Generally, a minimal solubility is at least achieved to obtain adesired reaction. As such, the metal oxide is preferably in the form ofa powder or a plurality of particles. Examples of the types of powdersthat can be used include, but are not limited to, flaked, angular,spherical, nodular, and blends thereof, and with shapes or variationsthereof. Examples of such preferred starting metal oxide powders includethose having mesh sizes of from about −10 to about −300 mesh and, morepreferably, from about −10 to about −200 mesh.

The metal oxide used in the present invention can be a product of thedecomposition and/or dissociation of a source compound. Preferably, thesource compound decomposes and/or dissociates into the metal oxide and aby-product. Preferably, the by-product is not deleterious to theformation of the perovskite-related ternary oxide. For example, themetal oxide can be Na₂O and the source compound can be Na₂CO₃ and theby-product can be CO₂. For this example, the decomposition/dissociationreaction can be written Na₂CO₃→Na₂O+CO₂.

Preferably, the metal oxide is different from the binary oxide.Preferably, the metal oxide is made from any material that can at leastbe partially suspended or solubilized or dissolved in the supercriticalfluid and can effectively react with the binary oxide to form thedesired ternary oxide.

The binary oxide can be in a shape and a size to effectively combinewith a metal hydroxide or other metal material. The binary oxide can bein the form of a powder, or as a solid film on a substrate. Preferably,the ratio of the metal oxide to the binary oxide can range from about1:3 to 3:1, such as about 2:1, 1:1, or 2:3. Preferably, when the binaryoxide contains or is made from tantalum and/or niobium, the metal oxideof the present invention is an alkali metal oxide. Preferably, when thebinary oxide contains or is made from titanium, the metal oxide of thepresent invention is an alkaline earth metal. Other metal oxides canalso be used alone or in addition to the alkali metal oxide. It ispreferred to use a high-purity metal oxide to avoid introduction ofimpurities when contacting the metal oxide with the binary oxide.Accordingly, the metal oxide preferably has a purity of at least about95%.

Preferably, when the binary oxide is made from niobium and/or tantalum,the preferred metal oxides are K₂O, Na₂O, and/or Li₂O, and when thebinary oxide is made from titanium, the preferred metal oxide is BaO.Preferably when the binary oxide is made from niobium and/or tantalum,the source compound that decomposes and/or dissociates into the metaloxide is Na₂CO₃, K₂CO₃, and/or Li₂CO₃. Preferably, when the binary oxideis made from titanium, the source compound that decomposes and/ordissociates into the metal oxide is BaCO₃.

The metal hydroxide can be any metal hydroxide capable of combining witha binary oxide. Preferably, the metal hydroxide is any material capableof fusing with the binary oxide. Preferably, the metal hydroxide is analkali hydroxide. Other metal hydroxides can also be used alone or inaddition to the alkali hydroxide. It is preferred to use a high puritymetal hydroxide to avoid introduction of other impurities when combiningthe metal hydroxide with the binary oxide. Accordingly, the metalhydroxide has a purity of at least about 95% and more preferably atleast about 99%.

The metal hydroxide can be in any shape or size. For instance, the metalhydroxide can be in the form of a powder or plurality of particles.Examples of the types of powders that can be used include, but are notlimited to, flaked, angular, spherical, nodular, and variations orcombinations thereof. Preferably, the metal hydroxide is in a shape anda size that can effectively be combined with the binary oxide.Preferably, the metal hydroxide is in a form of a powder, which moreeffectively combines/fuses with the binary oxide. In lieu of metalhydroxide, other metal materials as described above can be used alone orin combination. Examples of such preferred starting metal hydroxidepowders include those that have a mesh size of from about 60/100 toabout 100/325 mesh and from about 60/100 to about 200/325 mesh. Anotherrange of size is from about 40 mesh to about −325 mesh. The otherexamples of metal materials can have similar properties and/orparameters and/or characteristics.

According to one embodiment, the present invention includes contactingat least one binary oxide on a substrate with a metal oxide present in asupercritical fluid, wherein the metal oxide is different than thebinary oxide.

Another method to make the ternary oxide dielectric of the presentinvention is by contacting at least one metal oxide and at least onebinary oxide on a substrate with the supercritical fluid and aco-solvent. The co-solvent can be added before, during, and/or afteradding the supercritical fluid. The co-solvent can be added via an inletthat is separate from the inlet for the supercritical fluid, or it maybe added in the same inlet as the supercritical fluid. The co-solventcan be premixed with the supercritical fluid. The presence of theco-solvent can enhance the transport and reaction rates for the metaloxide with the binary oxide. Examples of metal oxides are the oxidesthemselves (e.g., Na₂O) or compounds capable of generating ordecomposing into metal oxides (e.g., Na₂CO₃, or NaOH, among others.)Examples of co-solvents are water and methanol. On a volume basis, thepreferred amount of co-solvent present in relation to the supercriticalfluid is from about 0.001 to 10% by volume. More preferably, the amountof co-solvent in relation to the supercritical fluid is from about 0.01to 1% by volume.

The supercritical fluid is preferably any supercritical fluid capable ofat least partially solubilizing, suspending, or dissolving the metaloxide. Preferably, the supercritical fluid that contacts the metal oxideand the binary oxide is polar and/or is used in the presence of aco-solvent. A polar supercritical fluid has a reasonable dielectricstrength, which enhances its ability to dissolve ionic materials such asthe metal oxide. However, supercritical fluids of the present inventioncan also be non-polar, such as supercritical CO₂. Examples ofsupercritical fluids that may be used in the present invention are HCl,H₂O, NH₃, SO₂, CO₂, and CO. The critical temperatures and pressures ofthe some supercritical fluids are shown below. Species T_(c)(K) T_(c)(C)P_(c)(Mpa) P_(c)(˜psi) HCl 324.7 52 8.31 1220 H₂O 647.1 374 22.06 3200NH₃ 405.5 132 11.35 1670 SO₂ 154.6 -118 5.043  741 CO₂ 304.1 30.9 7.7351138 CO 132.9 -140 3.499  510

Although the above-mentioned supercritical fluids may be used, certainsupercritical fluids are more common in use than others, namelysupercritical CO₂, supercritical CO, and supercritical H₂O. The criticaltemperature and pressure for CO₂ and CO are considerably less than thoseof H₂O, and thus the equipment requirements and capital expenses areless compared to those that use supercritical water. Batch reactions maybe performed, for instance, with supercritical CO₂, HCl, CO, or NH₃while maintaining the same margin of pressure safety.

Purification steps can be performed on the ternary oxide film that isformed on the substrate. These purification steps may include acidwashing and water washing to remove any impurities. The acid used forthe purpose of removing the impurities from the ternary oxide film canbe any acid capable of removing impurities from the ternary oxide film.Preferably, the acid is HF, HNO3, HCl, or H₃PO₄. The acid can have anypH that is capable of removing the impurities. Preferably, the acid hasa pH of from about 0 to about 5. Similar to acid washing, water can alsobe used to remove the impurities.

In another technique for making a ternary oxide dielectric, a reactantis combined with at least one supercritical fluid. Preferably, thereactant can be any composition that provides a base metal for theternary oxide and can be solubilized, suspended, or dissolved in thesupercritical fluid and react with the metal oxide. The reactant canalso be a gas that can be mixed in the supercritical fluid. Preferably,the metal part of the reactant is different than the metal of the metaloxide. Preferably, the metal of the reactant is a transition metalelement. One example of such a reactant is TaCl₅. It is preferred to usea high-purity reactant to avoid introduction of impurities whencontacting the reactant with the metal oxide. Accordingly, the reactantpreferably has a purity of at least about 95%, and more preferably atleast about 99%.

This method also includes water that is premixed with the supercriticalfluid. Alternatively, water may be added separately from thesupercritical fluid, before and/or after addition of the supercriticalfluid. The water is added for purposes of providing an oxide source forthe ternary oxide. It is preferred to use a high-purity water to avoidthe introduction of impurities during the reaction. Accordingly, thewater preferably has a purity of at least about 99%.

The present invention, as an option, permits the use of low temperaturesto make a ternary oxide dielectric with a perovskite structure whichprevents oxide diffusion and reaction of the substrate with impuritiesor solvents.

Substrates having a binary oxide layer are commonly available and can beobtained with the desired specifications. Alternatively, a substrate,such as an anode, can easily have a desired binary oxide layer formed onits surface using conventional methods, such as applying a voltage toform an anodic film. Substrates may also be relatively free of binaryoxide layer, insofar as is possible by cleaning with aqueous acids(e.g., HF). When preparing the metal oxide that is not of a sufficientsize to effectively include in the supercritical fluid, the metal oxidecan be crushed to a sufficient size in order to more effectivelydissolve in the supercritical fluid.

The supercritical fluid can be any supercritical fluid depending on thedesired characteristics of the final ternary oxide. Examples includeHCl, H₂O, NH₃, SO₂, CO₂, CO, and the like, or combinations thereof. Inone method, a gas is first introduced into an evacuated chamber. Morepreferably, the evacuated chamber is the reactor wherein the preparedmetal oxide and the substrate having a layer of binary oxide are placed.The temperature and the pressure of the gas inside the chamber are thenincreased to at least a temperature and a pressure sufficient for thegas to reach its supercritical stage. Preferably, the temperature of thegas is increased at a rate of from about 1° C./minute to about 20°C./minute until the gas reaches its supercritical temperature. In thepreferred embodiment, the temperature of HCl is increased to at leastabout 52° C., the temperature of the H₂O is increased to at least about374° C., the temperature of NH₃ is increased to at least about 132° C.,the temperature of SO₂ is increased to at least about −118° C., thetemperature of CO₂ is increased to at least about 30.9° C., and thetemperature of CO is increased to at least about −140° C. In thepreferred embodiment, the pressure of the gas is increased at a rate byadding the requisite amount of gas so that desired supercriticalpressure is obtained at the desired supercritical reaction temperature.Preferably, the pressure of the HCl is increased to at least about 1220psi, the pressure of the H₂O is increased to at least about 3200 psi,the pressure of NH3 is increased to at least about 1670 psi, thepressure of SO₂ is increased to at least about 741 psi, the pressure ofCO₂ is increased to at least about 1138 psi, and the pressure of CO isincreased to at least about 510 psi. Other pressures and conditions canbe used.

In preparing the ternary oxide dielectric, the size of the metal oxidecan be reduced (e.g., crushed) to a desired size and can be placed in areactor. Preferably, it is placed in the reactor at a location that caneasily be uptaken by the supercritical fluid. More preferably, the metaloxide is placed at the bottom of the reactor. The binary oxide, which ison a substrate, can also be introduced into the reactor at any time. Forexample, it can be introduced to the reactor before, during, and/orafter the metal oxide is placed in the reactor. The supercritical fluidcan also be introduced into the reactor at any time. Preferably, a gasis introduced into the reactor after the metal oxide and the substratehaving a layer of binary oxide have already been introduced into thereactor. The gas can then be brought to its supercritical state.Although the order of adding the supercritical fluid, the metal oxide,or the substrate having at least one layer of binary oxide to thereactor is not critical, preferably, the supercritical fluid is added tothe reactor after the metal oxide and the substrate having at least onelayer of binary oxide are introduced into the reactor.

Once the gas reaches its supercritical state, the supercritical fluidpreferably at least partially solubilizes, suspends, or dissolves themetal oxide and transports/carries or otherwise contacts the metal oxidewith the binary oxide located on the surface of the substrate. Becausethe supercritical fluid preferably has a low viscosity, high mobility,and/or high diffusion coefficient, the supercritical fluid speeds up theprocess of transporting the metal oxide to the binary oxide on thesurface of the substrate. The metal oxide in the supercritical fluid canthen react with the binary oxide located on the surface of the substrateto produce a perovskite-related dielectric film. The geometry, size, andstability of the dielectric film on the substrate can depend on thetemperature and the pressure of the supercritical fluid.

Once the ternary oxide film is formed, the supercritical fluid can thenbe removed or the substrate can be removed. The substrate having theternary oxide film can optionally be subjected to acid washing and/orwater washing or other cleaning techniques to remove any impurities.Preferably, the acid washing and the water washing are performed for asufficient time to remove all of the impurities from the ternary oxidefilm. The high stability of the ternary oxide film permits the use of afairly aggressive washing media at room temperature. Annealing atelevated temperatures may also be conducted to enhance performancecharacteristics. For example, the process can be carried out under highvacuum and the coefficients of thermal expansion are compatible for thefilm and the substrate.

The ternary oxide dielectric/perovskite related structure can also beobtained by using a source compound that releases gas (e.g.,Na₂CO₃→Na₂O+CO₂(gas) ) as the reaction progresses. The gas pressureinside the reactor can be allowed to increase as the reactionprogresses, or a portion of the gas can be vented to maintain thereactor at a marginally constant pressure (e.g., the desired operatingpressure, in psi, +/− 100 psi ).

When using a source compound that releases gas as the reactionprogresses and the gas is vented, a co-solvent may also be used. Sincesome of the co-solvent will be vented with the gas, additionalco-solvent may be added as the reaction progresses to make up for theco-solvent that is vented. Alternatively, additional make-up co-solventmay not be added, and the content of co-solvent present in thesupercritical fluid may diminish as the reaction progresses. Forexample, the content of co-solvent may diminish from the initial content(e.g., 1% by volume) to a lesser content (e.g., 0.1% by volume)

According to another embodiment, the present invention includes heatinga metal material at a temperature and a pressure sufficient to melt themetal material to form a molten metal material, and then contacting themolten metal material with a binary oxide, wherein the binary oxide isdisposed on the substrate. The metal material may be a metal oxide,metal salt, metal halide, metal hydroxide, metal carbonate, or metalnitrate, or combinations thereof. The molten metal material (e.g., LiOH)preferably has some capacity to dissolve at least some metal oxide(e.g., Li₂O) for reaction with the binary oxide (e.g., Nb₂O₅).

In preparing the metal material, if needed, it is crushed to a sizesufficient to effectively melt and produce a molten material.Preferably, the metal material is reduced into powder to produce moresurface area. The metal material can be subjected to two or morecrushings to achieve the desired uniform particle distribution for it toeffectively melt and produce the preferred molten metal material. Someexamples of such metal material include salts, such as KOH, NaF,Ba(OH)₂, Li₂CO₃, Li₂O, and K₂O. The metal material can then be heated toa sufficient temperature and for a sufficient time and at a sufficientpressure to melt the metal material.

Because it is desirable to have a high concentration of the metal oxidein the molten metal material, it is preferable to add other compositionsthat are capable of increasing the concentration of the oxide in themelt. Such additional composition can include other metal oxides thatmay or may not be identical to the metal oxide, for example, Li₂O inLiOH. The additional composition can be a size and a shape sufficient toincrease the concentration of the metal oxide in its molten state.Preferably, the size of this additional composition is macroscopic.

The binary oxide can be in a form of a film on the surface of thesubstrate. Preferably, the binary oxide is stabilized on the surface ofthe substrate using any suitable method. Preferably, the stabilizingmethod used changes the activity of the binary oxide relative to themolten metal oxide to stabilize the binary oxide on the surface of thesubstrate. Alternatively, the stabilizing method used changes theactivity of the incipient ternary oxide. One method involves anelectrical polarization process, for example. A voltage can be appliedto the substrate with the binary oxide, with the voltage related to thefree energy difference between the ternary and binary oxides.

The ternary oxide dielectric of this method can be formed by contactingthe binary oxide with molten metal oxide in a reactor, preferably acrucible reactor. The reactor is heated to a temperature sufficient forthe binary oxide film to uptake the metal oxide of the molten metaloxide to produce a ternary oxide. Preferably, the molten metal oxide andthe binary oxide on the surface of the metal substrate are heated to atemperature of from about 150 to about 1200° C., and more preferablyfrom about 250 to about 800° C. The binary oxide and the molten metaloxide are preferably reacted at a pressure of from about vacuum to about2 atmosphere absolute, and for a time sufficient for the binary oxidefilm to uptake the metal oxide to form the desired ternary oxide.Preferably, the reaction time is from about 1 to about 36 hours.However, the reaction time can vary significantly depending on thebinary oxide and the molten metal oxide.

According to another embodiment, the present invention includescontacting a binary oxide with the metal material and fusing themtogether upon heating, which forms into a solid material upon cooling;dissolving the solid material in a first solution, and disposing thefirst solution, or a derivative of the first solution onto a substrate;and heating the substrate having the solution disposed thereon undervacuum.

Metal materials, such as metal hydroxides, and preferably alkalihydroxides, are commercially available. Alternative metal material, asstated earlier, can include metal oxides, metal carbonates, and thelike. If the metal material is not of a sufficient size to effectivelybe combined or fused with the binary oxide, the metal material can becrushed. If needed, the metal material can be subjected to two or morecrushings to achieve the desired particle size and distribution. Themetal material is then preferably subjected to milling in order toobtain a desired particle size, which is of sufficient size to combineand fuse effectively with the binary oxide.

The binary oxide and the metal material can be mixed in a ratiosufficient to produce the final desired product. Preferably, the ratioof the binary oxide to metal material is about 1:1 or the amount ofmetal material can be higher. More preferably the ratio of binary oxideto the metal material is from about 1:1 to about 1:3. The mixture of thebinary oxide and the metal material can then be heated at a sufficienttemperature for a sufficient time for the binary oxide and the metalmaterial to combine or fuse. Preferably, the binary oxide and the metalmaterial are heated to at least the melting point of the compositionhaving the lower melting point.

The solid material formed by fusing the binary oxide and the metalmaterial can be cooled to room temperature (e.g., 25° C.) and can bedissolved in a first solution (e.g., water or ethanol, mixtures of thetwo, or others). In preparing the solid material to be dissolved in thefirst solution, if helpful, the solid material can be crushed to a sizesufficient to effectively be dissolved in the first solution.Preferably, the solid material is crushed into powder to produce moresurface area to be more effectively dissolved in the first solution. Ifdesired, the solid material can be subjected to milling in order toobtain the desired particle size to more effectively be dissolved in thefirst solution.

The first solution used to dissolve the solid material is preferablywater. Other solutions can be used. The minimum amount of the firstsolution should be sufficient to dissolve most or all of the solidmaterial. The first solution that dissolves the fused material can havea pH of from about 1 to about 13. Depending on the pH of the solution,different complex oxides can be formed.

The first solution can then be derivatized by dilution or by addition ofa second solvent (e.g., ethanol and the like). Preferably the fusedsolid material, in the first solution is then disposed or casted onto asubstrate, preferably a conductive substrate, to form a film. Anysuitable method for casting the aqueous solution on the metal substratecan be used. For instance, the substrate can be dipped into thesolution. Another method is to spray the solution on the substrate.Another method is to spin coat the substrate with the solution. Othermethods of disposing the aqueous solution onto the metal substrate arewell known in the art.

The ratio of the solution to the surface of the substrate can depend onthe application of the final product. The thickness of the film can becontrolled by any suitable method, for example, a multiple coatingmethod. In the multiple coating method, depending on the desiredthickness of the film, one or multiple coatings are applied to thesurface of the metal substrate. Another method to control the thicknessof the film is by modifying the viscosity of the solution. This can beaccomplished by varying the ratio of the fused solid material and thefirst solution that is capable of dissolving the fused solid material. Ahigher viscosity solution forms a thicker film on the substrate.Additionally, modifying the surface tension of the solution can alsoaffect the thickness of the film formed on the substrate. The surfacetension depends on the concentration of the solution. Other methods tocontrol the thickness of the film are well known in the art.

The metal oxide containing the solution can be heated to a temperaturesufficient to convert the solution having complex oxides to a ternaryoxide dielectric. The upper temperature limit can depend on theoxidizing conditions. Preferably, a metal substrate having at least onelayer of solution is heated to a temperature of from about 150 to about1400° C. Preferably, moderate temperatures (e.g., from about 150 toabout 300° C.) are used when heating the metal substrate with at leastone layer of the solution in an air containing atmosphere. Moderatetemperatures are used under these conditions because at highertemperatures the oxygen in the air atmosphere promotes oxidization ofthe electrically conductive substrate instead of converting the binaryoxide to a ternary oxide. Higher temperatures, up to about 1400° C., forinstance, can be used when heating the conductive substrate having atleast one layer of solution under vacuum conditions. It is preferred toheat the film on the substrate under vacuum conditions because there isno oxygen in the atmosphere to promote oxidization of the metalsubstrate and thus, only the binary oxide reacts with the metal materialto produce a ternary oxide dielectric film.

The substrate having at least one layer of solution is heated for a timesufficient to form a uniform ternary oxide dielectric film and tosatisfy the functional characteristics of the application. Preferably,the substrate and its film are heated from about 1 hour to about 36hours, and more preferably are heated for about 1 hour to about 6 hours.Preferably, the heating rate is controlled until all of the water in thesecond solution is evaporated and/or until any excess oxide(s) isvaporized. More preferably, the heating rate is from about 5 to about50° C./min until most or all the water in the aqueous solution isevaporated. The heating rate can be accelerated until the desiredtemperature and/or proper characteristics of the desired ternary oxidefilm is produced.

According to another embodiment, the present invention includes making aternary oxide dielectric by anodizing a metal to produce a binary oxideor layer on the metal, wherein the metal/binary oxide can be an anode.One way to obtain the ternary oxide is by contacting the binary oxidewith a molten metal containing one or more dissolved oxides. The moltenmetal may be molten alkali metals, alkaline earth metals, or mixturesthereof.

Anodization to produce the binary oxide on a substrate may be performedby an electrochemical method, as is familiar to those skilled in the artof producing dielectrics by anodization. The substrate is then contactedin a molten metal for 1 or less to 36 hours or more, preferably, 1 to 4hours. The substrate may be a foil, filament, or pressed part comprisingpowder or filaments.

The molten metal preferably is alkali metals, alkaline earth metals ormixtures thereof. The molten metal may be a bath that the substrate isimmersed in, or a film formed on the substrate by condensation of themetal vapor. The molten metal is exposed to oxygen gas or air to producemetal oxides. Preferably, the amount of oxygen or air is less than orequal to the amount of metal oxide that is soluble in the molten metal.Upon forming the solution of metal oxide in the molten metal, thedissolved metal oxide then reacts with the substrate comprising thebinary oxide to form the ternary oxide.

According to another embodiment, the present invention includesanodizing a binary oxide, wherein the binary oxide is an anode orpressed body, and the metal material is an electrolyte. The metalmaterial may be, but is not limited to, a metal hydroxide, metalcarbonate, or metal oxide, or mixtures thereof. The anodizing preferablyoccurs in an electrolyte, which preferably has some solubility for themetal oxide. Examples of electrolytes are metal oxides, metalhydroxides, metal carbonates, metal halides, and metal nitrates, amongothers.

Anodizing can be achieved by any suitable method, for example, bypassing an electrical charge between a first electrode and a secondelectrode which are disposed in an electrolyte. In this process, a firstelectrode can be partially or entirely made from a binary oxide, such asNbO. The first electrode is placed into the electrolyte, preferably ametal hydroxide, and more preferably, a molten salt. A second electrodewhich can be an inert electrode, can also be placed in the sameelectrolyte. In the preferred embodiment, the first electrode can bemade from any electrically conductive substrate that includes a layer ofthe binary oxide. To initiate the reaction, an oxide can be added to theelectrolyte, and a current is passed between the first and secondelectrodes. Once the reaction starts, excess oxides are generated whicheliminates the need to introduce more oxides to maintain the reaction.The reaction causes the binary oxide electrode or the electrodesubstrate having a layer of binary oxide to uptake the metal oxide inthe electrolyte to produce a layer of ternary oxide. The thickness ofthe ternary oxide dielectric layer can be controlled and determined bythe charge, current, or voltage passing between the first electrode andthe second electrode.

A similar process can also be used to produce ternary oxide dielectric.In this process, a binary oxide pellet(s) or powder is placed into anelectrically conductive basket or other container containing thecomposition (molten salt) and two inert electrodes. The binary oxidepellets are large enough not to pass through the basket. The process ofconverting the binary oxide to the ternary oxide are similar asdiscussed above. To initiate the reaction, an oxide is introduced intothe composition and a current is passed between the first and secondinert electrodes through the electrically conductive basket. The currentpassing between the two electrodes causes the composition (molten salt)to react with the binary oxide pellets/powder in contact with theelectrically conductive basket to produce a ternary oxide. As discussedpreviously, the thickness of the ternary oxide can be controlled anddetermined by knowing the current passing between the first electrodeand the second electrode and the duration of the reaction.

In various embodiments, the substrate and/or other components of thepresent invention, including the ternary oxides, and layers and filmsthereof, can contain conventional amounts or higher amounts of dopants(e.g., about 10 ppm to about 100,000 ppm), like alkaline earth dopants,transition dopants, alkali dopants, rare earth dopants, nitrogen,oxygen, phosphorus, sulfur, boron, and the like, and combinationsthereof.

In one embodiment of the present invention, the substrate is an anodewherein the binary oxide is present on the anode. The binary oxide canbe formed on the anode by any suitable technique such as by ananodization process which occurs prior to the reacting of the binaryoxide with a metal material to form the ternary oxide dielectric layer.Furthermore, the anode which contains the binary oxide and whichultimately is used to form the ternary oxide dielectric layer on theanode can subsequently be used as an anode in a capacitor usingconventional capacitor designs. The capacitor can be a solid capacitoror a liquid filled capacitor. The present invention provides a veryconvenient way to form a ternary oxide dielectric layer on an anode orother surface which has a multitude of benefits as described herein.

The substrate having the ternary oxide film can be cleaned as describedearlier. The perovskite ternary oxide dielectric layer is useful forcapacitors and other devices, and in particular is useful with anodesurfaces. Embodiments of the present invention include powder with aternary oxide layer, preferably a metal powder, like Ta or Nb, with aternary oxide layer as described earlier. The metal powder is preferablyhigh surface area powder, such as at least a BET of about 0.5 m²/g orhigher, and more preferably at least about 1.0 m²/g, such as from about1.0 m²/g to about 15 m²/g or more. The present invention furtherincludes an anode or pressed article with the ternary oxide layer of thepresent invention. The layer is preferably a coherent, uniform, and/orcontinuous film. Details of the type of capacitor and anodes that can beused in the present invention or adapted for the present inventioninclude U.S. Pat. Nos. 6,512,668; 6,500,763; 6,495,021; 6,479,857;6,458,645; 6,432,161; 6,430,026; 6,423,110; 6,423,104; 5,580,367;6,338,816; 6,348,113; 6,416,730; 6,420,043; 6,402,066; 6,380,577;6,373,087; 6,358,625; 6,146,959; 6,046,081; 6,040,975; 5,986,877;5,605,561; and 5,225,286, all incorporated in their entirety byreference herein.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

1. A method of making a ternary oxide comprising: reacting a binaryoxide with a metal material to form a ternary oxide dielectric layer ona substrate, wherein said metal material is different than said binaryoxide, wherein said metal material is a metal oxide, a metal carbonate,a metal nitrate, a metal halide, a metal hydroxide, a metal fluoride, orcombinations thereof.
 2. The method of claim 1, wherein said reacting isachieved in a reactor.
 3. The method of claim 1, wherein said binaryoxide comprises a transition metal oxide.
 4. The method of claim 3,wherein said transition metal oxide comprises Nb₂O₅, Ta₂O₅, TiO₂, orcombinations thereof.
 5. The method of claim 1, further comprisingforming said binary oxide on said substrate by an anodization processprior to said reacting.
 6. The method of claim 1, wherein said metalmaterial is an alkali oxide or an alkaline earth oxide, Li₂O, K₂O, Na₂O,BaO, or combinations thereof, and wherein said binary oxide is Nb₂O₅,Ta₂O₅, TiO₂, or combinations thereof.
 7. The method of claim 1, whereinsaid metal material is an alkali oxide or an alkaline earth oxide. 8.The method of claim 1, wherein said metal material is a metal oxide andincludes a metal to oxide ratio of about 2:1, 1:1, or 2:3.
 9. The methodof claim 1, further comprising generating said metal material bydecomposing a compound that produces said metal material.
 10. The methodof claim 9, wherein said compound is Li₂CO₃, Na₂CO₃, K₂CO₃, BaCO₃, orcombinations thereof.
 11. The method of claim 10, wherein saiddecomposing of said compound produces Li₂O, Na₂O, K₂O, BaO, orcombinations thereof respectively.
 12. The method of claim 1, whereinsaid substrate is a metal substrate.
 13. The method of claim 1, whereinsaid substrate is a valve metal substrate or valve metal suboxidesubstrate.
 14. The method of claim 1, wherein said substrate is aconductive metal or metal oxide substrate.
 15. The method of claim 1,wherein said substrate is a refractory metal substrate.
 16. The methodof claim 1, wherein said substrate is tantalum and said ternary oxide isa ternary tantalum oxide.
 17. The method of claim 1, wherein saidsubstrate is niobium and said ternary oxide is a ternary niobium oxide.18. The method of claim 1, wherein reacting comprises contacting asupercritical fluid with said metal oxide and said binary oxide, andwherein said binary oxide is disposed on said substrate.
 19. The methodof claim 18, wherein said metal oxide is at least partially solubilizedin said supercritical fluid.
 20. The method of claim 18, wherein saidsupercritical fluid comprises HCl, H₂O, NH₃, SO₂, CO₂, CO, orcombinations thereof.
 21. The method of claim 18, wherein saidsupercritical fluid is formed by introducing a gas into a reactor andthen placing said gas in a supercritical state.
 22. The method of claim18, wherein said supercritical fluid is introduced into a reactor havingdisposed therein said metal oxide, and said binary oxide on saidsubstrate.
 23. The method of claim 18, wherein said metal oxide ispresent with said supercritical fluid, and wherein said supercriticalfluid and said metal oxide are introduced into a reactor having disposedtherein said binary oxide on said substrate.
 24. The method of claim 18,wherein said supercritical fluid is present with at least oneco-solvent.
 25. The method of claim 24, wherein said co-solvent ismethanol or water.
 26. The method of claim 24, wherein said co-solventis present with said metal oxide, and wherein said supercritical fluidand said co-solvent are introduced into a reactor having disposedtherein said binary oxide on said substrate.
 27. The method of claim 24,wherein said co-solvent is introduced with said supercritical fluid intoa reactor having disposed therein said metal oxide, and said binaryoxide on said substrate.
 28. The method of claim 24, wherein saidco-solvent is introduced after said supercritical fluid into a reactorhaving disposed therein said metal oxide, and said binary oxide on saidsubstrate.
 29. The method of claim 24, wherein said supercritical fluidand said co-solvent are premixed to form an inlet stream that isintroduced into a reactor having disposed therein said metal oxide, andsaid binary oxide on said substrate.
 30. The method of claim 24, whereinsaid co-solvent and said supercritical fluid are present at a volumeratio of from about 1:10,000 to about 1:10.
 31. The method of claim 24,wherein said metal oxide is placed in a reactor and wherein said metaloxide is a solid.
 32. The method of claim 24, wherein said co-solventcauses an increase in solubility, transport characteristics, or both insaid metal oxide.
 33. The method of claim 1, wherein an electrical fieldis applied to said substrate during said reacting.
 34. The method ofclaim 1, wherein said reacting comprises: heating said metal material ata temperature and a pressure sufficient to melt said metal material toform a molten metal material; and contacting said molten metal materialto said binary oxide, wherein said binary oxide is disposed on saidsubstrate.
 35. The method of claim 34 wherein said metal material is ametal oxide.
 36. The method of claim 34, further comprising stabilizinga film of said binary oxide on said substrate by applying a voltage tosaid substrate.
 37. The method of claim 34, wherein said temperature isfrom about 150 to about 1200° C.
 38. The method of claim 34, whereinsaid pressure is from about vacuum to about 2 atmosphere absolute. 39.The method of claim 34, wherein said molten metal material comprises amolten salt.
 40. The method of claim 34, wherein said binary oxidecomprises a transition metal oxide.
 41. The method of claim 40, whereinsaid transition metal oxide comprises Nb₂O₅, Ta₂O₅, TiO₂, orcombinations thereof.
 42. The method of claim 34, further comprisingforming said binary oxide on said substrate by an anodization processprior to said reacting.
 43. The method of claim 34, wherein saidsubstrate is a metal substrate.
 44. The method of claim 34, wherein saidsubstrate is a valve metal substrate or valve metal suboxide substrate.45. The method of claim 34, wherein said substrate is tantalum and saidternary oxide is a ternary tantalum oxide.
 46. The method of claim 34,wherein said substrate is niobium or niobium suboxide and said ternaryoxide is a ternary niobium oxide.
 47. The method of claim I, whereinreacting comprises: fusing said binary oxide with said metal material toform a solid material; dissolving said solid material in a firstsolution; disposing said first solution or a derivative of said firstsolution onto said substrate; and heating said substrate having saidfirst solution disposed thereon or an evaporated film of the firstsolution disposed thereon under vacuum.
 48. The method of claim 47,wherein said contacting comprises coating, spraying, dipping, exposingto vapors, or combinations thereof.
 49. The method of claim 47, whereinsaid solid material comprises a fused material.
 50. The method of claim47, wherein said first solution comprises water.
 51. The method of claim1, wherein reacting comprises anodizing said binary oxide, wherein saidbinary oxide comprises an anode, in an electrolyte comprising said metalmaterial.
 52. The method of claim 51, wherein said electrolyte comprisesa metal hydroxide.
 53. The method of claim 51, wherein said electrolytecomprises a molten salt.
 54. The method of claim 51, wherein said binaryoxide comprises NbO, and said electrolyte comprises NaOH.
 55. The methodof claim 51, wherein said electrolyte further comprises an oxide ion toinitiate said reacting.
 56. The method of claim 51, wherein said anodecomprises a metal having a layer comprised of said binary oxide.
 57. Themethod of claim 1, wherein said reacting comprises anodizing said binaryoxide, wherein said binary oxide comprises an anode, and contractingsaid binary oxide with at least one molten metal containing at least onedissolved oxide.
 58. An article comprising a ternary metal oxide layerlocated on at least one substrate.
 59. The article of claim 58, whereinsaid substrate is a valve metal substrate or valve metal suboxidesubstrate.
 60. The article of claim 58, wherein said substrate comprisesTa and/or Nb and/or NbO.
 61. The article of claim 58, wherein saidternary metal oxide comprises dopant levels of nitrogen, oxygen, boron,sulfur, phosphorus, or mixtures thereof.
 62. The article of claim 58,wherein said ternary metal oxide comprise at least one dopant.
 63. Thearticle of claim 58, wherein said ternary oxide has the formula AMO₃,wherein A is an alkali metal or alkaline earth and M is a metal.
 64. Thearticle of claim 63, wherein AMO₃ is a solid solution of at least twoternary oxides.
 65. The article of claim 58, wherein said ternary oxideis Na_(x)K_((1−x)) NbO₃, KTa_(x) Nb_((1−x))O₃, Na_(x) K_((1−x))Ta_(y)Nb_((1−y))O₃, Ta_(2x) Nb_((2−2x))O₅, wherein x is from 0 to 1 and y isfrom 0 to
 1. 66. A pressed metal article comprising a perovskite-relatedternary oxide dielectric layer on a pressed substrate.
 67. The pressedmetal article of claim 66, wherein said pressed metal substrate is atleast one valve metal or valve metal suboxide.
 68. The capacitor ofclaim 66, wherein said anode comprises at least one valve metal oralloys thereof.
 69. The pressed metal article of claim 66, wherein saidmetal article is an anode.
 70. The pressed metal article of claim 66,wherein said perovskite-related ternary oxide is LiNbO₃, KNbO₃, KTaO₃,or BaTiO₃, NaNbO₃, NaTaO₃, or a perovskite-related compound that is asolid solution of two or more perovskite ternary oxides.
 71. The articleof claim 58, wherein said ternary oxide is LiNbO₃, KNbO₃, KTaO₃, orBaTiO₃, NaNbO₃, NaTaO₃, or a compound that is a solid solution of two ormore ternary oxides.
 72. The pressed metal article of claim 66, whereinsaid pressed metal substrate is Nb.
 73. The pressed metal article ofclaim 66, wherein said pressed metal substrate is Ta.
 74. A capacitorcomprising a perovskite-related ternary oxide dielectric layer on ananode.
 75. The capacitor of claim 74, wherein said anode comprises Taand said perovskite-related ternary oxide is a ternary tantalum oxide.76. The capacitor of claim 74, wherein said anode comprises Nb and saidperovskite-related ternary oxide is LiNbO₃, KNbO₃, Na NbO₃, NaTaO₃, orcombinations thereof.
 77. The capacitor of claim 74, wherein said anodecomprises Ta and said perovskite-related ternary oxide is NaTaO₃ orKTaO₃.
 78. The capacitor of claim 74, wherein said anode comprises Nb orNbO, and said perovskite-related ternary oxide is a ternary niobiumoxide.
 79. A capacitor comprising a perovskite-related ternary oxide.80. A capacitor comprising a perovskite-related compound that is a solidsolution of two or more perovskite-related ternary oxides.
 81. An anodecomprising a perovskite-related ternary oxide dielectric layer.
 82. Ananode comprising a dielectric layer comprising a perovskite-relatedcompound that is a solid solution of two or more perovskite-relatedternary oxides.
 83. The method of claim 1, wherein said substrate is ananode.
 84. The method of claim 1, wherein said substrate is an anode andsaid binary oxide is formed on said anode by an anodization processprior to said reacting.
 85. An anode having a dielectric layer formed bythe method of claim
 83. 86. An anode having a dielectric layer formed bythe method of claim
 84. 87. A capacitor comprising the anode of claim85.
 88. A capacitor comprising the anode of claim 86.